1. Field of the Invention
This invention relates to end plugs for pipes and, more particularly, to polymeric plugs of the type that are cemented into the ends of plastic pipe for use in leak testing.
2. Description of Related Art
Pipe end plugs are frequently used for leak testing of plastic pipe installations and to keep debris out of plastic pipes during construction. The plugs are typically injection molded from a thermoplastic material such as polystyrene and have annular flanges that are cemented in place on the end of a section of plastic pipe. Once the pipe has been filled with a fluid and the flow system has been tested for leaks, a circular "knockout" disc in the plug is removed to permit the passage of fluid through the end of the pipe into other fittings or flow lines to which the pipe end is subsequently connected.
Conventional plastic pipe end plugs comprise a knockout disc that traverses the pipe bore at a point recessed slightly inside the end of the pipe. The knockout disc is typically molded as a unitary part of the plug and is connected to the inside annular flange of the plug by a continuous, circumferentially extending web having a reduced thickness as compared to the thickness of either the disc or flange portions of the plug. The thinned plastic web is designed to be strong enough to withstand the anticipated test pressure, but thin enough to facilitate removal from the plug flange by the application of force such as a hammer blow when it is time for the knockout plug to be removed.
One disadvantage commonly experienced in using conventional plastic pipe end plugs is that the knockout disc falls into the pipe when removed from the plug. Similarly, If the disc shatters instead of breaking away cleanly when struck with a tool such as a hammer, pliers or screwdriver, the blow can drive plastic fragments further into the bore. A pipe plug is therefore needed that comprises an easily removable disc which cannot fall into the pipe upon removal.
Another disadvantage commonly experienced in using conventional pipe end plugs is that the plug and disc are opaque. This opacity precludes the user from observing whether or not the test fluid, typically water, has sufficiently filled the piping system to reach and fully contact the plugged pipe end. In the past, users have often drilled through or otherwise punctured the end plug during a leak test in order to determine whether the underside was wetted. A pipe end plug is therefore needed that will permit the user to determine by visual inspection whether or not the underside of the knockout disc is wetted by a contained fluid.